(1) Field of the Invention
The present invention relates to a nonmagnetic material for producing parts or coatings adapted for highly wear and corrosion intensive applications, said material comprising preformed particles made of tungsten carbide which are embedded in a metal phase made of a Ni-based alloy.
The invention also relates to nonmagnetic component, especially for use in a drill string.
(2) Description of Related Art including information disclosed under 37 CFR 1.97 and 1.98
Furthermore, the invention relates to a method for the manufacture of such a component by applying a coating on a surface of a substrate adapted to form a component for highly wear and abrasion intensive applications by providing a nonmagnetic raw material in powder form or wire form, melting the material and depositing it on said surface of the substrate.
The drilling of holes or bores into underground formations and particularly, the drilling of oil and gas wells, is typically accomplished using an elongated “drill string” which initially carries the drill bit or other cutting tool, and which is constructed from a number of sections of tubular drill pipe which are coupled at their ends. As the drill bit penetrates deeper or further into an underground formation, additional sections of drill pipe are added to the drill string.
It is conventional practice to line the wall of a bore hole with steel piping as the length of that bore hole progressively increases. This steel piping is generally known as a bore hole “casing”. The casing lines the bore to prevent the wall from caving in and to prevent seepage of fluids from the surrounding formations from entering the wellbore. The casing also provides a means for recovering the gas or the oil if the well is found to be productive.
A drill string can have a considerable length, and it is relatively flexible, being subject to lateral deflection, especially at the regions between joints or couplings. Lateral deflections can cause contacts between the drill string and the casing. In addition, the drilling operation may be along a curved or angled path, commonly known as “directional drilling”. Such directional drilling, especially, causes frequent contact between portions of the drill string and the casing.
It will immediately be realized that the drill string, which frequently contacts the surrounding bore hole casing, inevitably causes frictional wear, increased shock and abrasion to itself, and similar wear or other damage to the surrounding casing. Additional wear and corrosion results from the abrasive slurry passing between the drill string and the casing even if they are not in direct contact.
Furthermore, drilling string components are often exposed to highly corrosive media such as multipercent sodium chloride solutions, magnesium chloride solutions as well as hydrogen sulfide and the like. Therefore, a high resistance to corrosion, especially stress corrosion cracking is required.
In order to eliminate or reduce the frictional wear, protection is provided along the length of the drill pipe string. This protection takes the form of welded, sprayed or brazed overlays applied around the circumference of the drill collar, to form “hardbands”. The overlays may be applied directly to the drill pipe, or may also be applied to an annular body that surrounds the drill pipe
It was also suggested that the drill string, or a part of it, is formed from rigid alloys provided with low friction bearing means between the drill string and the casing. The low friction bearing means may be coatings or inserts made of a low friction alloy, low friction ceramic or magnetic elements. For example, a low friction alloy insert could be formed from steel with ceramic elements inserted therein.
In a paper titled “Hardbanding for Drilling Unconsolidated Sand Reservoirs”, presented at the IADC/SPE Asia Pacific Drilling Technology” held in Jakarta, 9-11 Sep. 2002, by J. Barrios, C. Alonso, E. Pedersen, A. Bachelot and A. Broucke, it is reported that tungsten carbide grains are used to prepare tungsten carbide-steel composites in order to increase the hardness of hardbanding material applied to a contact surface of a drill string. The tungsten carbide grains shall resist melting and alloying during welding of the hardbanding. Steel is used as a matrix material merely to stick the tungsten carbide grains on the contact surface. Instead of steel other matrix materials in form of alloys were tested and it was found that the harder the matrix material the higher the wear resistance in tungsten carbide hardbanding materials.
Other suitable alloys to give protection from wear and corrosion have long been known. For example, Nickel-based alloys with additives of chromium and molybdenum are successfully involved in many branches of industry for the purposes of thermal spraying and welding, as described for example in DE 196 28 346 A1.
U.S. Pat. No. 6,482,534 B2 discloses a spray powder comprising a metal phase made of a Ni or Ni-based alloy powder which has a particle size of from 6 to 63 μm and which comprises from 75 to 95 wt % of a ceramic phase made of a powder consisting of preformed tungsten carbide particles and at least one chromium carbide powder selected from the group consisting of Cr3C2, Cr7C3 and Cr23C6. This powder is capable of forming a sprayed coating having extremely high toughness and impact resistance and also having excellent corrosion resistance and wear resistance in a wet environment.
In addition to its mechanical properties for withstanding mechanical stress and wear and chemical corrosion, some drilling string components should possess nonmagnetic or at least less magnetic characteristics. The reason is that during the implementation of exploratory or prospecting bores, the position and direction of the drill heads is established by magnetic measurement. Since bores extend to increasingly greater depths, an especially exact position determination is required, which is especially difficult to establish for directional bores. Moreover, the measurements of magnetic effects are susceptible to distortion, not least because of the masses of ferrous materials incorporated in the drill string and bottom-hole assembly. Distortion of magnetic measurements can give rise to unacceptable errors in the determination of position and direction of the drilling, with undesirable consequences.
Distortion of magnetic measurements in the region of the instrumentation arising from inherent magnetism should be as low as possible. This means that the drilling string components, which are located in the immediate proximity of the measuring instrumentation should exhibit the most minute degree of magnetic anomalies.
Besides that, distortion of magnetic measurements in the region of the instrumentation of conventional drill string and bottom-hole components can also be mitigated by locating the instrumentation in a special section of the drill string, which is fabricated of non-magnetic alloy.
For evaluation of the non-magnetic properties the so-called API (American Petroleum Institute;) specification may be used (“Specification for Rotary Drill Stem Elements”; page 23). The API specification specifies that the magnetic permeability shall be less than 1.010, and that the maximum deviation from a uniform magnetic field shall not exceed +/−0.05 microtesla. If a material meets these requirements it can be approved for use on non-magnetic materials. A practicable test method on magnetizability of a drill stem is described in EP 0 014 195 A1.
From Austrian Patent No. 214,466, there is known a nonmagnetic austenitic chromium manganese steel alloy for manufacturing nonmagnetic drilling string components containing each in percent by weight, carbon up to a maximum of 0.12, silicon up to a maximum of 0.6, manganese 17.0 to 19.0, chromium 11.5 to 13.0, nickel 1.5 to 2.0, molybdenum 0.4 to 0.6, nitrogen 0.1 to 0.15, the remainder being iron and the usual accompanying elements.
The materials known in the art are not suitable to meet all requirements with regard to wear and corrosion resistance as well as to nonmagnetic properties as explained hereinbefore.
It is therefore an object of the present invention to provide a material that is suitable to produce parts or coatings having a high corrosion and wear resistance, and which at the same time is nonmagnetic at ambient and drilling temperatures.
It is a further object of the invention to provide a component for use in a drill string showing low inherent magnetism and therefore, contributing as less as possible to a distortion of magnetic measurements.
With respect to the nonmagnetic material for producing parts or coatings adapted for highly wear and corrosion intensive applications as specified above, this object is achieved according to the invention by a material characterized by having a weight portion of the tungsten carbide particles which is in the range between 30 w % and 65 wt. % and wherein the Ni-based alloy is a Nickel-Chromium-Molybdenum alloy comprising: (in wt. %):
Cr11.0-30.0  Mo5.0-25.0 Fe 0-10.0B0-5.0Co0-2.5
The nonmagnetic material according to the invention is characterized by a metal phase made of a Ni-based alloy comprising at least an amount of chromium and molybdenum as specified above and a low maximum content of iron, boron or cobalt, which will be explained below in more detail. This alloy forms a relatively soft matrix when compared to the hardness of the preformed tungsten carbide particles embedded therein. The alloy may contain additional elements, especially C, Mn, Si, V, W, Cu, B, P and N as long as these elements do not negatively affect the non magnetic property of the ally. The overall content of those additional elements is less than about 25 wt. %, preferably less than about 18 wt. % and most preferred less than about 10 wt. % as it is explained below in more detail.
The use of Ni-based alloys with additives of chromium and molybdenum to give protection from corrosion has long been known. Such alloys are disclosed for example in U.S. Pat. No. 6,027,583 A. However, such an alloy may be relatively soft and therefore not beneficial for wear and abrasion intensive applications.